Electrophoretic procedures provide for the analytic or preparative separation of mixtures based on molecular size, charge, and/or affinity for the electrophoresis matrix. Analytic and preparative procedures require that the separation of the position of molecules proceeds to a given degree, long enough in time that components of the mixture are resolved from each other, and short enough that desired components are not lost by running off the end of the separation matrix. Traditionally, visible of fluorescent markers, with molecular properties similar to those of difficult to visualize samples, are added to the mixture, the positions of these marker molecules are monitored by a human operator, and electrophoresis is terminated when said markers reach positions indicating that the desired separation has taken place. This provides the most accurate indication of the progress of separation, since variabilities in the voltage, current, temperature, and matrix pore size affect the mobility of the markers to the same extent that they do the samples. Thus, under variable conditions of electrophoresis, marker mobility is a better predictor than time of sample mobility. A limitation of this strategy is that a human operator must be present to periodically monitor the migration of the molecular markers and terminate electrophoresis at the appropriate time, which can range from minutes to days, depending upon application.
A typical electrophoresis apparatus consists of a slab of electrophoresis matrix and rigid support on one or more sides of the matrix. Matrix and supports are usually constructed of relatively clear materials so that molecular markers can be seen or visualized. An electric power supply is connected to the matrix via electrodes such that a direct current can be maintained across the slab. Electrodes generally consist of a conductive metal immersed in a conductive liquid. Samples mixtures are loaded into indentations, termed wells, formed at one end of the matrix. Samples are drawn toward the opposite end of the matrix by electrostatic interactions at a rate related to their physical properties. As in the case of the Automatic Isolator of Blood Plasma disclosed in U.S. Pat. No. 4,354,116 issued to Tsukamoto et al. Oct. 12, 1982, this arrangement provides access for the photodetector in this invention to take the place of human eyes in the monitoring of molecular marker or sample positions and for electronic circuitry to automate electrophoresis control (See FIG. 1).
The photoelectric elecrophoresis controller of the present invention eliminates the tedium of a human operator periodically checking on the progress of separation as well as the risk that often priceless analytical samples are lost due to carelessness. This controller provides these advantages in a much less complicated and much less expensive manner than the Computer-analyzed Vidicon Scanner system disclosed in U.S. Pat. No. 3,723,712 entitled Method for Agglomeration Measuring and Control issued to Komline et al. Mar. 27, 1973. The embodiment described herein is particularly versatile and convenient. Because the preferred embodiment optionally compares the light falling on a pair of spaced broad-spectrum Cadmium Sulfide photocells, said embodiment is able to detect the presence of virtually any sample, stained sample, or reference molecular dye marker that the eye can see and which the photocells can detect; it is thus compatible with a wide variety of electrophoresis protocols involving samples and molecular markers with different spectral properties. Because detection is based on a comparison to a reference photocell, virtually any broad-spectrum light source, present even at a varying intensity, including ambient light, will suffice for accurate detection; thus, the small photodetector occupies space on only one side of the electrophoresis apparatus, making it compatible with an apparatus of any thickness. Furthermore, detection by comparison can offer greater sensitivity than a system relying on absolute detection.